Japanese Patent Application Laid-Open (kokai) No. 2015-190012 discloses a technique in which the number of crystal grains in a cross-section in the longitudinal direction of a wire containing Ir, as a wire that can be used for an electrode (tip) of a spark plug, is set to be 2 to 20 per 0.25 mm2. In the technique disclosed in Japanese Patent Application Laid-Open (kokai) No. 2015-190012, the areas of grain boundaries where oxidation easily occurs at high temperature as compared to crystal are decreased by reducing the number of crystal grains, so that high-temperature oxidation wear resistance is improved.
In the above conventional technique, however, it is doubtful whether an effect of inhibiting a reduction in volume of a tip by spark discharge (spark wear) is exhibited. Improvement of spark wear resistance is required for tips of spark plugs.
The present invention has been made to meet the above requirement. An advantage of the present invention is a spark plug that can improve the spark wear resistance of a tip, and a manufacturing method therefor.